Liquid Crystal displays (LCDs) has the advantages of compact, low power consumption and radiation-less. The LCDs are developed rapidly over the past years and are in a leading position in the present flat-panel display market. Currently, the LCDs are employed in products of various sizes and cover most electronic products in our information society, such as Liquid Crystal Televisions, High Definition Digital TVs, computers (desktop computers and notebooks), mobile phones, PDAs, GPSs, in-vehicle displays, projector displays, video recorders, digital cameras, digital watches, calculators, electrical instruments, meters, public displays and virtual displays. Such a position is non-achievable by any conventional display.
However, as liquid crystal materials do not produce light by themselves, a LCD is a passive display device and requires external light sources to realize display with a certain brightness and colors. According to the method of using the external light sources, the LCDs generally comprise Reflective LCDs (RE-LCDs), Transmissive LCDs (TS-LCDs) and Transflective LCDs (TR-LCDs). TR-LCDs may use the display mode of RE-LCDS in the case of having enough ambient light, which overcomes the disadvantage of blur display under strong ambient light of the TS-LCD and reduces the power consumption; while in a dark circumstance a backlight may be switched on. By using the TS-LCD display mode, the disadvantage of not able to display anything in dark environment is overcome.
In a TR-LCD, liquid crystals and phase difference films are normally combined. Specifically, in a display portion of the TR-LCD, liquid crystal elements are sandwiched between a pair of phase difference films to form a laminated structure, polarizing films or protection films are further laminated to outer sides of the laminated phase difference films. The phase difference films that can be used together with the liquid crystal elements may produce phase differences by using difference in refraction indices, thereby improving viewing angles of the LCDs.
In conventional technologies, the TR-LCDs are normally realized by making an orientation of liquid crystals in liquid crystal films, an orientation of a liquid crystal layer and a slow axis direction of the phase difference film on top of the liquid crystal layer to be in the same direction, that is to say, the three layers are parallel to each other and having a 90 degrees or 45 degrees angle with a direction (which is normally a direction of a line connecting both eyes of a user under normal viewing situation) vertical to the orientation of the liquid crystal layer (refer to Japanese Patent publication No. 2004-125830A). Such a three layer parallel structure may maintain wide viewing angle of the LCD while realizing high contrast ratio. However, such a structure may cause the problem of color cast, especially yellow color cast, which is quite serious. The reason for the color cast issue is that the liquid crystal is a birefringent material, when being viewed from an oblique direction, refractive indices for light of different wavelengths are different, and the differences in refractive indices are different as well. After being refracted by the liquid crystal, the phase retardation value of the light are different, which will generate difference in the light intensity after being polarized by the polarizer, thereby producing color cast. In the U.S. patent application publication No. 2002/0159007A1, the color cast problem with the reflective LCDs are solved by a design which provides a polarizer, a quarter wavelength (¼λ) phase difference film and a half wavelength (½λ) phase difference film. This technique may achieve quite good color cast correction effect for RE-LCDs; however, the actual effect at the transmissive region of the TR-LCDs is not ideal.